Keesom interactions

4) Wilhelmus Hendrik Keesom, 1876-1956. Dutch physicist, professor in Utrecht and Leiden. 

As we can see, the distance dependence has changed from proportional to D for the fixed dipoles to for the thermally averaged dipole-dipole interaction. Again, the interaction energy decreases as for increasing temperature. 

Calculate the free energy between two freely rotating water molecules 1 nm apart in vacuum at room temperature. 

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There are three types of interactions that contribute to van der Waals forces. These are interactions between freely rotating permanent dipoles (Keesom interactions), dipole-induced dipole interaction (Debye interactions), and instantaneous dip le-induced dipole (London dispersion interactions), with the total van der Waals force arising from the sum. The total van der Waals interaction between materials arise from the sum of all three of these contributions. 

Abbreviations are in parentheses. The dd interactions are also known as Keesom interactions di interactions are also known as Debye interactions ii interactions are also known as London or dispersion interactions. Collectively, dd, di and ii interactions are known as van der Waals interactions. Charge transfer interactions are also known as donor-acceptor interactions. 

The dipole-dipole interactions, frequently referred to as Keesom interactions, are historically included in the van der Waals interactions, even though they are purely electrostatic. For molecules that are free to orient themselves, the dipole-dipole interactions must be averaged over the molecular orientations, as the angular dependence of the interaction energy is comparable to the Boltzmann energy kBT (Israelachvili 1992, p. 62). With the averaging of the Keesom... 

This is the dipole-dipole interaction energy, often termed the orientation or Keesom interaction. Notice that it depends on the product of the squares of both dipole moments, but is inversely proportional to distance to the sixth power. This is a very short-range... 

Almost all interfacial phenomena are influenced to various extents by forces that have their origin in atomic- and molecular-level interactions due to the induced or permanent polarities created in molecules by the electric fields of neighboring molecules or due to the instantaneous dipoles caused by the positions of the electrons around the nuclei. These forces consist of three major categories known as Keesom interactions (permanent dipole/permanent dipole interactions), Debye interactions (permanent dipole/induced dipole interactions), and London interactions (induced dipole/induced dipole interactions). The three are known collectively as the van der Waals interactions and play a major role in determining material properties and behavior important in colloid and surface chemistry. The purpose of the present chapter is to outline the basic ideas and equations behind these forces and to illustrate how they affect some of the material properties of interest to us. 

Compounds that undergo only vdW interactions (London plus Debye plus Keesom interactions) are commonly referred to as apolar. Examples include alkanes, chlorinated benzenes, and PCBs. 

One limitation of the one-solubility parameter model is that it assumes that the solute can only interact with the organic matter through London forces. Although this assumption may be reasonable for SOM, DOM is typically more polar and can participate in other types of van der Waals interactions. These include permanent dipole-induced dipole (Debye) and permanent dipole-permanent dipole (Keesom) interactions in which the degree of binding that occurs depends on the polarizability of the DOM (Gauthier et al., 1987 Uhle et al., 1999). To account for these types of interactions Chin and Weber (1989) segregated the solubility parameter terms into three components to account for all these different types of molecular interactions to... 

The van der Waals force between atoms consists of three different dipole induced forces, the Keesom interaction, the Debye interaction and the London interaction. 

Keesom interaction occurs when a permanent molecular dipole creates an electric field, which orients other permanent dipoles in such a way that they will attract each other. 

Keesom interactions of permanent dipoles whose mutual angles are, on average, in attractive orientations ... 

This extraction precisely reproduces the same London, Debye, and Keesom interactions, including all relativistic retardation terms that had been effortfully derived in earlier formulations. These interactions are distinguished by whether they involve the interaction of two permanent dipoles of moment //.uipoie, or involve an inducible polarizability aind. A water molecule, for example, has both a permanent dipole moment and inducible polarizability. The contribution of each water molecule to the total dielectric response is a sum of the form of Eqs. (L2.163) and (L2.173) in mks units,... 

Molecules bearing a permanent-dipole moment Think of the interaction between two fairly strong dipoles, /xc ipoie = 2 D = 2 x 10 18 esu cm, slightly larger than the 1.87-D moment of a water molecule.11 Let this molecule be approximately the size of a water molecule, i.e., 3 A across so that the point-molecule approximation would apply at separations much greater than 3 A. In emits of kT the Keesom interaction is... 

Physisorptive interactions can be classified by the component forces giving rise to the overall intermolecular attractions. The predominant forces include hydrogen bonding and van der Waals forces, which is a broad classificatimi covering dispersion (London), dipole-induced dipole (Debye), and dipole-dipole (Keesom) interactions [95]. The nature of these forces is illustrated in Figure 5.6. 

The chapter ends with a short outline of the theory of the temperature-dependent Keesom interactions in polar gases. 

D18.4 There are three van der Waals type interactions that depend upon distance as l/r6 they are the Keesom interaction between rotating permanent dipoles, the permanent-dipole-induced-dipole-interaction, and the induced-dipole-induced-dipole, or London dispersion, interaction. In each case, we can visualize the distance dependence of the potential energy as arising from the Mr dependence of the field (and hence the magnitude of the induced dipole) and the Mr3 dependence of the potential energy of interaction of the dipoles (either permanent or induced). 

The dipole-dipole (Keesom) interaction comes about from the fact that on the average, two freely rotating dipoles will align themselves so as to result in an attractive force, similar to that commonly observed with bar magnets. In order to calculate the net dipole-dipole interaction, it is necessary to examine all the possible orientations of the dipoles with respect to one another. It is also necessary to determine any jr - effects due to the field associated with a point charge, in order to determine the net effect when amorphous solids are placed side by side. We also need to consider what happens if the dipoles can reorient in each other s fields. 

The Boltzmann angle-averaged interaction potential is generally referred to as the orientation or Keesom interaction and represents one of the three 6th power of distance relationships involved in the total van der Waals interaction. 

The Keesom interaction energy for freely rotating dipoles is obtained from an expansion series. That series becomes inaccurate as the interaction energy approaches a value of kT. Calculate the dipole moment at which this occurs at room temperature and a separation distance of 0.28 nm ... 

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